11 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| El Dorado | 1 | 16,396 | 17,700 | -1.57% | 1,012 | 16 | City |
| Smackover | 2 | 1,559 | 1,627 | -0.89% | 358 | 4 | City |
| Norphlet | 3 | 709 | 759 | -1.39% | 347 | 2 | City |
| Junction City | 4 | 474 | 501 | -1.25% | 417 | 1 | City |
| Huttig | 5 | 424 | 453 | -1.4% | 142 | 3 | City |
| Calion | 6 | 407 | 431 | -1.21% | 380 | 1 | City |
| Strong | 7 | 393 | 415 | -1.26% | 246 | 2 | City |
| Mount Holly | 8 | 230 | 102 | 6.98% | 82 | 3 | CDP |
| Lawson | 9 | 149 | 80 | 7.19% | 45 | 3 | CDP |
| Urbana | 10 | 149 | 168 | 7.19% | 80 | 2 | CDP |
| Felsenthal | 11 | 83 | 86 | -1.19% | 56 | 1 | Town |
El Dorado is the largest city in Union County, with a population of 16,396.
Felsenthal is the smallest city in Union County, with a population of 83.
There are 11 cities in Union County, Arkansas.